Phosphorus utilization in rainbow trout (Oncorhynchus mykiss) fed practical diets and its consequences on effluent phosphorus levels
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Excessive dietary phosphorous (P) concentrations in effluents from aquaculture present a major environmental problem. We therefore studied the effect of dietary P and vitamin D3 on P utilization by rainbow trout-fed practical diets and on P concentrations in the soluble, particulate and settleable components of the effluent from fish tanks. Rainbow trout (average weight: 78 g, initial biomass: 13 kg in 0.7 m3 tanks) were fed for 11 weeks, practical diets that varied in total P, available P, and vitamin D3 concentrations. Soluble, particulate (10–200 μm) and settleable (>200 μm) P in the effluent were sampled every 0.5–6 h for 1–3 days in the third and eleventh weeks of the experiment. Trout in all diets more than doubled their weight after 11 weeks. Increasing the concentrations of available dietary P from 0.24% to 0.88% modestly enhanced growth rate. Feed conversion ratio (FCR) and biomass gain per gram P consumed decreased as dietary P concentrations increased. Carcass P, daily P gain, and plasma P concentrations were lower in fish fed with low P diets. Soluble P concentrations in the effluent peaked immediately after and again 4–6 h after feeding, and is a linear function of available dietary P. No soluble P would be produced during consumption of diets containing less than 0.22±0.02% available P. Above this dietary concentration, soluble P would be excreted at 6.9±0.4 mg/day/kg for each 0.1% increase in available dietary P. Particulate P concentrations in the effluent were independent of dietary P concentrations. Settleable, presumably fecal, P concentrations tended to increase with dietary P concentrations. In trout fed with low P (0.24% available P, 0.6% total P) diets, 60% of total dietary P were retained by the fish and the remaining 40% were excreted in the effluent as settleable P (20–30%) and particulate or soluble P (10–20%). In trout fed with high P (0.59–0.88% available P; 0.9–1.2% total P) diets, 30–55% of total dietary P was retained by fish, and the remaining 15–25% appeared in the effluent as settleable P, 20–55% as soluble P, and 5–10% as particulate P. Vitamin D3 did not affect fish growth nor effluent P levels. Physicochemical management of aquaculture effluents should consider the effect of diets on partitioning of effluent P, the peaks of soluble P concentration following feeding, and the contributions of particulate P to total P in the effluent. Increasing our understanding of how dietary P is utilized and is subsequently partitioned in the effluent can contribute significantly towards alleviating this important environmental and industry problem.
CitationColoso, R. M., King, K., Fletcher, J. W., Hendrix, M. A., Subramanyam, M., Weis, P., & Ferraris, R. P. (2003). Phosphorus utilization in rainbow trout (Oncorhynchus mykiss) fed practical diets and its consequences on effluent phosphorus levels.
This project was supported by USDA grant no. 01-35102-09881, USDA grant no. 94-38500-0044 (Northeastern Regional Aquaculture Center) and NSF-IBN9985808. We thank J. Choi, S. Basantes, E. Gagiu, T. Proctor, W. Jodun and P. Farrell for expert technical assistance, as well as F. Jarder of the Centralized Analytical Laboratory of the Aquaculture Department, Southeast Asian Fisheries Development Center for proximate analyses of the diets. We are indebted to Drs. N. McDaniel and S. Sugiura for critically reviewing the manuscript.
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Book chapterGA Gonzales - In T Bagarinao (Ed.), Research Output of the Fisheries Sector Program, 2007 - Bureau of Agricultural Research, Department of AgricultureThis study determined the concentration of key pollutants carried by agricultural run-off from the drainage area of Imbang River, Negros Occidental over a two-year period. The quantities loaded into the river were estimated to assess the contribution of agriculture to the degradation of the river. Agricultural production in sugarcane and rice plantations in the area relied on chemicals to control pests and enhance production. Run-off from agricultural land contained an average 0.2 ppm phosphate, 0.2 ppm ammonia, 0.02 ppm nitrite, and 1.7 ppm nitrate from fertilizer inputs and other sources. The run-off also had 7.4 ppm biochemical oxygen demand, 465 ppm total solids, 296 ppm total suspended solids, 0.4 ppm settleable solids, plus traces of organochlorine pesticides. The concentrations of all these potential pollutants were not alarming or dangerous, although on occasion, some exceeded the tolerable limits. However, increasing reliance on fertilizers often leads to intensified use and related problems. Likewise, the continuing use of chemicals to control field pests is of serious concern given that residues are easily carried by run-off to the nearest waterway and passed on and magnified through the food chain. The health of farm workers who routinely handle these products is at risk. Apart from commercial fertilizers, farm lands received organic wastes from domestic and industrial sources. Most farmers maintained farm animals such as carabaos, goats, and sheep that were allowed to graze on the fields after crops had been harvested. Grazing animals frequently left surface deposits of manure. Some farmers on occasion used sugar mill wastes as fertilizers and road fillers in the haciendas. Moreover, household wastes including human excreta were commonly disposed on nearby fields. The contributions of animal and human wastes to the total load of nutrients could be substantial but difficult to quantify given the manner of production and the varying composition of the wastes. Indeed, agricultural run-off transports non-point pollutants from so many poorly defined sources.
Dietary P regulates phosphate transporter expression, phosphatase activity, and effluent P partitioning in trout culture RM Coloso, K King, JW Fletcher, P Weis, A Werner & RP Ferraris -
Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology, 2003 - Springer VerlagPhosphate utilization by fish is an important issue because of its critical roles in fish growth and aquatic environmental pollution. High dietary phosphorus (P) levels typically decrease the efficiency of P utilization, thereby increasing the amount of P excreted as metabolic waste in effluents emanating from rainbow trout aquaculture. In mammals, vitamin D3 is a known regulator of P utilization but in fish, its regulatory role is unclear. Moreover, the effects of dietary P and vitamin D3 on expression of enzymatic and transport systems potentially involved in phosphate utilization are little known. We therefore monitored production of effluent P, levels of plasma vitamin D3 metabolites, as well as expression of phosphatases and the sodium phosphate cotransporter (NaPi2) in trout fed semipu diets that varied in dietary P and vitamin D3 levels. Mean soluble P concentrations varied markedly with dietary P but not with vitamin D3, and constituted 40–70% of total effluent P production by trout. Particulate P concentrations accounted for 25–50% of effluent P production, but did not vary with dietary P or vitamin D3. P in settleable wastes accounted for <10% of effluent P. The stronger effect of dietary P on effluent P levels is paralleled by its striking effects on phosphatases and NaPi2. The mRNA abundance of the intestinal and renal sodium phosphate transporters increased in fish fed low dietary P; vitamin D3 had no effect. Low-P diets reduced plasma phosphate concentrations. Intracellular phytase activity increased but brushborder alkaline phosphatase activity decreased in the intestine, pyloric caeca, and gills of trout fed diets containing low dietary P. Vitamin D3 had no effect on enzyme activities. Moreover, plasma concentrations of 25-hydroxyvitamin D3 and of 1,25-dihydroxyvitamin D3 were unaffected by dietary P and vitamin D3 levels. The major regulator of P metabolism, and ultimately of levels of P in the effluent from trout culture, is dietary P.
Effect of dietary phosphorus and vitamin D3 on phosphorus levels in effluent from the experimental culture of rainbow trout (Oncorhynchus mykiss) RM Coloso, SP Basantes, K King, MA Hendrix, JW Fletcher, P Weis & RP Ferraris -
Aquaculture, 2001 - ElsevierExcessive phosphorus (P) levels in aquaculture effluents violate federally mandated limits and pose a serious threat to the freshwater environment. In rainbow trout culture, effluent P probably originates as fecal and metabolic waste product because assimilation of dietary P is relatively low. We therefore decreased dietary P and increased dietary vitamin D3 levels, methods that enhance P assimilation in mammals, in purified and semi-purified trout diets, then monitored effluent P. Soluble effluent P reached a peak right after feeding and returned to baseline levels in between feeding times. The peak and average concentrations of soluble P in the effluent were mainly influenced by dietary P. Average P in fecal dry matter also decreased with dietary P. Neither dietary P nor vitamin D3 under the conditions of the experiment had significant effects on whole body P content but P deposition (as a percentage of P intake) decreased with increased dietary P. The dietary combination of low P and high vitamin D3 decreased soluble and fecal P levels in the effluent indicating a strategy whereby effluent P concentrations can be reduced by regulation of P metabolism.